The present invention generally relates to an endoscope. More specifically, the present invention relates to systems and methods for calibrating an endoscope.
Computer-assisted systems and methods now provide real-time navigation during surgical procedures, including analysis and inspection of three-dimensional (3-D) anatomical images from magnetic resonance (MR) and computed tomography (CT) data). Endoscopic technology has also undergone rapid development, providing lightweight endoscopes able to be used in small body cavities. Endoscopes are however able to display only visible surfaces, and are also limited by their inability to provide views of the interior of opaque tissue. The combination of both endoscopic and computer-generated 3-D images has the potential to provide the previously unavailable capability of overlaying volumetrically reconstructed patient images onto the endoscopic view of the surgical field. This technique could permit surgeons to look beyond visible surfaces and provide “on-the-fly” 3-D and two-dimensional (2-D) information for planning and navigational purposes. Due to the many parameters involved in the function of an endoscope, however, multiple small errors in the settings of the device may have relatively large and cumulative effects on the final discrepancy between the position of the overlaid endoscopic images and the patient's anatomy. For this reason, precise calibration of the endoscope and accuracy testing of the calibrated endoscope is necessary to ensure surgical quality.
Thus, there is a need for systems and methods of calibrating an endoscope, an endoscopy system, and/or an augmented endoscopy system.
Image-guided or augmented endoscopy, as described above, is a technique where computer-generated virtual reality representations of endoscopic views can be combined with real-world views to produce “augmented reality.” This technique typically requires that the endoscope be tracked in space by well-known methods such as electromagnetic (EM) and/or optical navigation systems. For example, an endoscope calibration fixture may be tracked in space or calibration markers on the fixture may be in a known location with respect to the tracking system.
An advantage of augmented endoscopy is to assist in the visualization of critical structures that may not be evident in real-time endoscopic video images by addressing the relative loss of stereoscopic depth perception and orientation associated with endoscopy. By calibrating the endoscope's position and line of sight to the navigation system and calibrating the endoscope's optical lens parameters (camera calibration), the co-registration of the computer-rendered 3-D virtual representation of the endoscope's field of view could be performed with the endoscopic video image. Depth perception may be augmented, and therefore, healthy and diseased tissue not directly visible to the endoscope may be displayed.
However, the endoscope's optical lens parameters, such as focal length, principal point, radial and tangential distortion, pixel scaling, and field of view, may vary with the magnification of the endoscope. Typically, the magnification of the endoscope is adjusted by rotating a zoom control on the endoscope camera. Unlike surgical microscopes, which typically include optical encoders to determine the amount of zoom or magnification, systems and methods for detecting endoscope magnification do not exist.
Thus, there is also a need for systems and methods for detecting endoscope magnification and calibrating the endoscope, the endoscopy system, and/or the augmented endoscopy system accordingly.